One of the current trends in the automobile industry is to lower vehicle weight to help achieve better fuel economy, thus helping to meet fuel economy standards and to offset the higher fuel prices. Another trend is that there is a broader range of vehicle models, which in turn reduces the volume of vehicles produced on a per model basis. Liftgates are traditionally made from stamped steel panels that are heavy and have a high tooling cost. Sheet Molding Compound (SMC) is an alternative to steel for the inner and outer panels of the liftgate. Using SMC has several manufacturing concerns related to the material and process. Steel and SMC liftgates have a mass penalty over thermoplastics. There are also styling restrictions with traditional sheet metal components. Thermoplastic composite type materials used for liftgate applications also have difficulty meeting customer performance specifications.
Another concern with the manufacture of liftgates is that typical lifgates are manufactured as a relatively flat or smoothly contoured panel, with structural reinforcements such as ribs being added onto the panel. This will also add weight and increase manufacturing complexity as well.
One solution to this problem has been the 2008 Nissan Murano composite liftgate system, which has helped to satisfy the weight savings and the tooling cost concerns, but utilizes a typical bolt in small steel reinforcement at the latch which secures one end of the liftgate to the vehicle. This does not meet the higher load requirements desired in some applications, such as the latch pull test.
Accordingly, there exists a need for a composite liftgate which is both lightweight, as well as structurally sound enough to meet various load requirements.